MK1 heated bed and different power supplies

04 Aug12

MK1 heated bed and different power supplies

I couldn't reach the temperatures I wanted for printing ABS using my MK1 heated bed. The MK1 is a PCB with fat copper traces and simply running power through it makes it heat up due to the resistance of the metal. For ABS to stick properly, I need the heated build surface to reach about 120 Celcius within reasonable time. Today I've tested three different solutions and written up the results in a spreadsheet. The graph above actually makes sense even though you would think that the 425 watt computer PSU would be better than the 360 watt industrial PSU.

The reason is that the KDM 1U 425 power supply isn't really 425 watt. It's split into two "rails" - each with something like 212 watts. This is apparently common for computer PSU's. I asked KDM if I could "pool" the two outputs, but they advised against that. Depending on construction, that can make the PSU unstable to such a degree that it burns and I don't want that… Another thing is that the KDM does not turn the fan on when needed. Not a good sign!

Based on the above I'll use the 360 watt PSU for now. Only drawback is that it's from China and not CE certified. It still seems better built than the KDM though as it turns the fan on when needed. I won't be printing ABS without watching over the machine. I'll also stay with the relay approach even though other users with heated beds don't think it's required. They are probably right, but keeping it won't hurt? I like this extra layer of abstraction and I'll still keep the original (external) PSU to drive the Ultimaker itself. The new PSU is 5 cm tall, so I'll need to print some "legs" for the Ultimaker to ensure proper airflow.


04 August 2012 at 11:15 pm

6 Responses to MK1 heated bed and different power supplies

  1. avatar photo
    Bertho Boman 05 August 2012 at 1:18 am #

    Great that you resolved the problem.  That is timely verification of my earlier post today.  I always stay away from the PC power supplies.
    I would not worry too much about lacking CE certification.  Usually the competition in the switching power supply market requires good performance or the companies will not be in business.

  2. avatar photo
    Frans de Jong 05 August 2012 at 9:20 am #

    No problems without relay?
    But there was mentioning of the power switch not functioning any more. And not switching on the HBP power after switching on the main powwer..
    So there are restrictions.
    I go for the relay as well, but the socket is not yet here.
    cheers, Frans

  3. avatar photo
    Reklama Raciborzu 08 August 2012 at 6:19 am #

    First I’d love your website design!
    Simple and clean for reading.
    To how many degree you want heating your bed?

  4. avatar photo
    Nick Steve 09 August 2012 at 10:27 am #

    The reason is that the KDM 1U 425 power supply isn’t really 425 watt. It’s split into two “rails” - each with something like 212 watts…. is it making the things to run slowly or what?

  5. avatar photo
    simon wilkinson 18 August 2012 at 7:32 am #

    I had the same experience, it definitely splits the output and this has resulted in significantly reduced output.

  6. avatar photo
    Max "Generator" Stanford 29 August 2012 at 3:51 pm #

    It would be nice to get a reliable 360 PSU generator working for you that was either made here for CE certification or at least a foreign one that was compliant.